Jennifer Garner poses at the premiere of "The Odd Life of Timothy Green" at El Capitan theatre in Hollywood, California August 6, 2012. (REUTERS/Mario Anzuoni)

LOS ANGELES - Joel Edgerton whoops with joy when he sees Jennifer Garner walk into a conference room here. That seems to be the general effect she has on everyone.

Garner and Edgerton (Animal Kingdom) are co-stars in a film called The Odd Life of Timothy Green, a magical fable about parenting and the many ways that children come into our lives. Garner, in real life recently back at work after the birth of her third child with husband Ben Affleck, plays a wife and first-time mother in the movie: "Yeah "¦ If I couldn't get THIS role," she jokes.

Garner, 40, who is tall and beautiful, says that one of the things she likes about The Odd Life of Timothy Green (in theatres Wednesday) is that the movie tells some truths about parenting.

"It doesn't shirk from the fact that sometimes when you're trying your hardest as a parent, that's when you're screwing up the most."

With daughters aged six and three and an infant son, Garner is currently living in what she calls "mama land." Like all working mothers, she tries to find balance.

"I kind of take it one thing at a time. I do get pickier with every kid," she says of the roles that interest her, "but I'm ambitious in a different way now than I was before. I'm ambitious for my family and I sneak off and do something to fill me up. And I've realized, having been home as long as I have been, which is a huge luxury, that I do need this job. I do need to do this ... and it's got to be something I need to do in order to leave my kids and do it. And my partner's pretty busy, so we can't all just get up and go."

Domestic bliss aside, Garner says she'd be willing to take on some edgier work.

"I 'd like to do some action or something where I shock myself a little bit. I was just visiting my husband's set in Puerto Rico, and it's a lot of the same camera guys as on The Kingdom. They see me," she says, adopting a tough-guy male voice, "and they're like, 'Hey Jen! What's up! Remember that fight scene!' And I felt like I was a different person from the person they were talking about. And I thought, 'I kind of need to do something like that for myself.' "

Garner got her big break kicking butt as one of the leads in TV's Alias and made her presence known in film from around 2000 onward, thanks to roles in Daredevil, Pearl Harbor, Catch Me If You Can and 13 Going On 30. Her other major movies include The Kingdom, Juno, Valentine's Day and Arthur, among others.

Would she do the action-packed work of an Alias again?

"Of course I would!" she exclaims. "I had the time of my life. I don't know if I'd be as cavalier about jumping off a building again," she says, laughing, "but the rest of it, for sure."

Garner grew up in Charleston, W. Va., one of three daughters of an English teacher mom and a chemical engineer dad. She was an avid ballet student growing up.

"So what there was to do in my little town was ballet and community theatre and the same woman ran both and still does," says the actress. "That's what there was to do in Charleston. I loved to perform and I loved to be backstage. And I still do."

Garner describes an idyllic childhood in Charleston but says that a bit of sibling rivalry is probably what led to her career as an actress.

"My older sister is so exceptional, and I definitely grew up in her shadow," says Garner. "She's so beautiful, and she was valedictorian, and incredibly academically successful -- in our state! And recognized all the time, and when she composed a little piece on the piano, she played it with our state symphony, and she's just one of those gifted people."

Performing was one way to differentiate herself from her sister and claim something for herself.

"I worship her, and I've never had an issue with her," adds Garner. "And I have to say, my sisters have never once made me feel they have an issue with the luck I've had."

Meanwhile, Garner says she's very happy in mama land but knows a return to work is inevitable.

"I'll just feel ready when the right thing comes along," she says, cheerfully. "And when the right thing comes along, I'll do it."